I have 105, 400x400 arrays. I want to stack these arrays on top of each other, in any number of ways, i.e, 400x400x3, 400x400x10, 400x400x105....

The main idea is that they will be a 3D array.

Essentially what needs to be done, is after I stack them, let's say in a 400x400x3 array, I need to write a loop that will break the array into cubes (basically sub matrices) of my specification. For example, take my 400x400x3 array and break this by [4,4] blocks where the output is a single matrix of 100x100, where each number of the new 100x100 is the summation value of the numbers in each [4,4] block. Is that clear?

I tried to use the blockprock function, and I don't understand the 'fun' function handle. It instructed me to use 'block_struct' and 'block_struct.data' and I have no idea what those are or how to use them. My array is simply numeric and I thought block_struct.data was an array that contained multiple values, not just numeric values? Please help and thanks in advance!

My guess is that BLOCKPROC passes that structure instead of just the
specified piece of your matrix into the function because for image
processing applications that extra information may be useful. The data field
of that struct array contains just the specified piece of your matrix.

> My array is simply numeric and I thought block_struct.data was an array
> that contained multiple values, not just numeric values?

BLOCKPROC will call this function four times: once with the upper left
2-by-2 block of M stored in block_struct.data, once with the upper-right,
once with the lower-left, and once with the lower-right.

> See the Definitions section of the BLOCKPROC documentation page for
> information about the fields contained in the block_struct struct array.
>
> http://www.mathworks.com/help/images/ref/blockproc.html
>
> My guess is that BLOCKPROC passes that structure instead of just the
> specified piece of your matrix into the function because for image
> processing applications that extra information may be useful. The data field
> of that struct array contains just the specified piece of your matrix.
>
> > My array is simply numeric and I thought block_struct.data was an array
> > that contained multiple values, not just numeric values?
>
> Take a look at this example:
>
> >> M = reshape(1:16, [4 4]);
> >> blockproc(M, [2 2], @(block_struct) mean(block_struct.data(:)))
>
> BLOCKPROC will call this function four times: once with the upper left
> 2-by-2 block of M stored in block_struct.data, once with the upper-right,
> once with the lower-left, and once with the lower-right.
>
> --
> Steve Lord
> slord@mathworks.com
> To contact Technical Support use the Contact Us link on
> http://www.mathworks.com

Thanks for the reply... does that mean blockproc it only goes to those 4 places you mentioned--upper left-right-lower left-right-- and not through the entire matrix to create blocks? I am currently researching this and I am getting different answers from every different site I look at. Thanks in advance for all of your help.

> Thanks for the reply... does that mean blockproc it only goes to those 4
> places you mentioned--upper left-right-lower left-right-- and not
> through the entire matrix to create blocks? I am currently researching
> this and I am getting different answers from every different site I look
> at. Thanks in advance for all of your help.

Why don't you go to the source? What do you need any other site than
the TMW documentation?

" ...
B = blockproc(A,[M N],fun) processes the image A by applying the
function fun to each distinct M-by-N block of A and concatenating
the results into B, the output matrix. fun is a function handle ..."

If you're still uncertain, create a small matrix of known values that
you can hand compute the result and try it and see what you get...

A=reshape([1:16],4,4); % would be a likely candidate for 2x2 processing

"Matthew Balint" <mjbalint2@gmail.com> wrote in message
news:l1ab4u$n4e$1@newscl01ah.mathworks.com...
>> See the Definitions section of the BLOCKPROC documentation page for
>> information about the fields contained in the block_struct struct array.
>>
>> http://www.mathworks.com/help/images/ref/blockproc.html
>>
>> My guess is that BLOCKPROC passes that structure instead of just the
>> specified piece of your matrix into the function because for image
>> processing applications that extra information may be useful. The data
>> field of that struct array contains just the specified piece of your
>> matrix.
>>
>> > My array is simply numeric and I thought block_struct.data was an array
>> > that contained multiple values, not just numeric values?
>>
>> Take a look at this example:
>>
>> >> M = reshape(1:16, [4 4]);
>> >> blockproc(M, [2 2], @(block_struct) mean(block_struct.data(:)))
>>
>> BLOCKPROC will call this function four times: once with the upper left
>> 2-by-2 block of M stored in block_struct.data, once with the upper-right,
>> once with the lower-left, and once with the lower-right.
>>
>> --
>> Steve Lord
>> slord@mathworks.com
>> To contact Technical Support use the Contact Us link on
>> http://www.mathworks.com
>
>
> Thanks for the reply... does that mean blockproc it only goes to those 4
> places you mentioned--upper left-right-lower left-right-- and not through
> the entire matrix to create blocks? I am currently researching this and I
> am getting different answers from every different site I look at. Thanks
> in advance for all of your help.

Well, in a 4-by-4 matrix there are only four nonoverlapping 2-by-2 blocks:
upper left, upper right, lower left, and lower right. If you tried this with
a 6-by-6 matrix there would be nine blocks: upper left, upper center, upper
right, center left, etc. For a 10-by-20 the result would be 5-by-10, but I'm
not going to try to come up with names for each of those positions ;)

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